The present invention relates to magnetic tape data storage. More particularly, the present invention relates to recording methods and systems for recording servo patterns on magnetic tape.
It is common to provide magnetic tape write/read head assemblies having one or more write/read transducer elements positioned transverse to the intended path of a magnetic recording medium, e.g., tape, for writing data on and reading data from parallel tracks on the tape. It is also known to include servo information on at least some of the parallel tracks and provide servo transducer elements on the recording/playback head for reading such information to enable control of the lateral position of the head assembly, thereby dynamically maintaining the respective transducer elements of the head assembly relative to tape track. With the use of servo control, data track widths can be made significantly narrower and the data capacity of the recording medium can therefore be increased.
Various techniques for providing servo tracks have been previously employed. For example, it is known to provide dedicated servo tracks on the medium at the time of manufacture, e.g., pulse recording servo information in the factory.
There are a substantial number of different servo track configurations for providing servo control. For example, one such servo pattern is described in U.S. Pat. No. 5,448,430 to Bailey, et al., entitled xe2x80x9cTrack Following Servo Demodulation,xe2x80x9d issued Sep. 5, 1995, which is useable with an IBM 3590 magnetic tape subsystem for writing/reading data to/from magnetic tape. As described therein, the servo pattern includes multiple servo areas which each include two outer tracks having a recorded servo pattern of one frequency located on either side of a middle track which has a different recorded servo pattern of a second frequency. Such a servo pattern attempts to minimize errors in the writing/reading of data to/from magnetic tape by effectively positioning a multi-track magnetic tape head relative to such magnetic tape. Conventionally, such servo patterns have been written utilizing pulse recording processes. In such processes, pulse generation circuits are used to generate write currents for driving servo writers to write servo patterns on the magnetic tape.
Pulse recording processes tend to require a relatively large bandwidth in the write driver used to generate drive currents for driving write elements to pulse record servo patterns. As such, the pulse recording process of servo information in servo tracks on magnetic tape tends to be relatively slow. With large quantities of magnetic tape being written in a factory, such slow servo recording rates are undesirable.
Further, generally, servo recording requires optimization of servo track positioning, e.g., the positioning of one or more servo track edges as perceived by a servo read head. Such servo track positioning is dependent on various factors, including, but clearly not limited to, actual physical servo track position, magnetization of the servo tracks by the recording fields, and spacing loss between servo record/read heads and the tape. In many servo recording techniques, it is difficult to compensate for variations with respect to such factors. As such, additional techniques to record servo tracks to provide some compensation for such variations are needed.
The present invention uses bias recording to record servo patterns on magnetic tape. With use of bias recording, a faster recording process is provided relative to conventional pulse recording processes.
A servo pattern recording method according to the present invention includes providing a servo band along at least a portion of a length of a tape. Bursts of a first signal are recorded in a first servo track of the servo band along the length of the tape and a second signal, e.g., a continuous signal, is recorded in at least a second servo track of the servo band along the length of the tape. The second servo track is recorded adjacent to the first servo track and at least one of the first signal and the second signal is recorded using a bias signal at a bias frequency summed with a record signal at a record frequency.
In one embodiment of the method, recording of the bursts in the first servo track includes recording the bursts using a first bias signal, e.g., a continuous signal, at a first bias frequency summed with bursts of a first record signal at a first record frequency and recording the second signal in at least the second servo track includes recording the second signal using a second bias signal at a second bias frequency summed with a second record signal at a second record frequency.
In another embodiment of the method, the method includes recording the bursts in the first servo track by driving a first write element in a first position with a first servo track write current that is a summation of a first servo track bias current and a first servo track record current. In a like manner, recording a continuous second signal in at least the second servo track includes driving a second write element in a second position with a second servo track write current that is a summation of a second servo track bias current and a second servo track record current.
Another servo pattern recording method according to the present invention includes providing at least one servo band along at least a portion of a length of a tape. Bursts of a first signal are recorded in an inboard servo track of the servo band using an inboard bias signal at an inboard bias frequency summed with bursts of an inboard record signal at an inboard record frequency. A continuous second signal is recorded in each of a first and second outboard servo track of the servo band. Each continuous second signal is recorded using an outboard bias signal at an outboard bias frequency summed with an outboard record signal at an outboard record frequency. The first outboard servo track is adjacent a first edge of the inboard servo track along the length of the tape and the second outboard servo track is adjacent a second edge of the inboard servo track along the length of the tape.
In one embodiment of the method, recording the bursts of the first signal in the inboard servo track includes driving a first write element with an inboard current that is a summation of an inboard bias current and an inboard record current. Likewise, recording the continuous second signal in each of the first and second outboard servo tracks includes driving second write elements with outboard currents that are a summation of an outboard bias current and an outboard record current.
In another embodiment of the method, the method includes determining the inboard and outboard bias currents by measuring servo read output amplitude for a plurality of servo patterns written using a plurality of bias currents with the other currents set to predetermined current levels. The bias currents are selected as a function of peak servo read output amplitude of the measured servo read output amplitudes.
In yet another embodiment of the method, the method includes determining the outboard record current as a function of a target servo read output amplitude. Further, the inboard record current may be determined as a function of a target inboard servo track width.
A servo pattern recording system for recording a servo pattern in at least one servo band along at least a portion of a length of a tape is also described. The system includes apparatus for recording bursts of a first signal in a first servo track of the servo band along the length of the tape and apparatus for recording a second signal, e.g., a continuous signal, in at least a second servo track of the servo band along the length of the tape. The second servo track is recorded adjacent to the first servo track and at least one of the first signal and the second signal is recorded using a bias signal at a bias frequency summed with a record signal at a record frequency.
In one embodiment, the apparatus for recording the bursts in the first servo track records the bursts using a first bias signal at a first bias frequency summed with bursts of a first record signal at a first record frequency. Further, the apparatus for recording the second signal in at least the second servo track records the second signal using a second bias signal at a second bias frequency summed with a second record signal at a second record frequency.
Another servo pattern recording system according to the present invention includes one or more write elements; a bias frequency generator operable to generate at least one bias frequency signal; an inboard frequency generator operable to generate at least one inboard frequency signal; an outboard frequency generator operable to generate at least one outboard frequency signal; amplitude control circuitry operable to modify the amplitude of the at least one bias frequency signal, the at least one inboard frequency signal, and the at least one outboard frequency signal; and burst control logic circuitry connected to the inboard frequency generator to provide for burst inboard frequency signals therefrom.
Control circuitry is operable to control the application of a bias frequency signal modified by the amplitude control circuitry and the application of burst inboard frequency signals modified by the amplitude control circuitry to at least a first output drive circuit to drive at least one of the write elements to record bursts of a first signal in an inboard servo track of at least one servo band along at least a portion of a length of a tape. Further, the control circuitry is operable to control the application of a bias frequency signal modified by the amplitude control circuitry and the application of an outboard frequency signal modified by the amplitude control circuitry to at least a second output drive circuit to drive at least one of the write elements to record a continuous second signal in first and second outboard servo tracks of the servo band. The first outboard servo track is adjacent a first edge of the inboard servo track along the length of the tape and the second outboard servo track is adjacent a second edge of the inboard servo track along the length of the tape.